The Brooks Glycerin Max was designed to feel like you’re running on the moon

They feel like a cartoon on my feet. Like if I look down, I won’t see a pair of shoes from the U.S.’s most popular running shoe brand, Brooks, but some Wile E. Coyote contraption of springs and duct tape. This is the Glycerin Max ($200, out on October 5th), the tallest-stacked sneaker that Brooks has ever made. And what is certainly the softest shoe my knees have ever met. “I originally told the team, it’s like running on the moon,” says Carson Caprara, SVP of footwear at Brooks. Rise of the foam-y shoe Ever since Adidas launched its foamy Ultraboosts in 2015 and Nike formalized thick, energy returning foam stacks for its Alphafly marathon shoes in 2017, running shoes have trended more maximal, using a combination of foams from the aircraft industry and even carbon fiber plates to help you bounce back with every stride. The promised payoff was originally speed, as Nike shoes broke marathon records. But as companies like Hoka and Brooks incorporated such technology, they chipped away at Nike’s dominance in the running market by realizing the benefits could be about more than performance. They could be about the sensation of running: comfort and recovery. (This idea is so powerful that Jeremy Renner started wearing Brooks while recovering from his own brush with death—before he inked a sponsorship deal with the company.) With the Glycerin Max, Brooks wanted to push the sensation of plushness to its extreme—to make what Caprara calls a Cadillac for your feet, a shoe that felt as marshmallowy on impact as possible—without making it feel like you were stuck in a pile of melted s’mores. The way that Brooks delivered that was by creating its tallest foam shoe ever—the heel is 36mm tall (which is nearly an inch and a half!)—with two flavors of foam that balance comfort and performance. “[It’s about] how much cushion you can provide before it actually starts becoming a negative experience,” says Caprara. “We’ve done some prototypes where we’ve gone really crazy high, and there’s a certain point where you reach diminishing returns, and then it becomes like, ‘oh, man, this thing’s like a freaking brick.’ Or, ‘I feel like I can’t my foot can’t move the shoe.’ Or you just feel like you’re sinking. And nobody likes that feeling over a period of time.”  Two foams, one mold In turn, the midsole of the Glycerin Max is made by firing two different chemistries of foam into one injection mold, which are then injected with nitrogen, inflating the material into countless little bubble springs. In photos, the yellow foam you see is a smaller cell foam, built for firmness and responsiveness. The surrounding white foam has noticeably bigger cells—it looks almost like plain old styrofoam—which are squishier and deform more when you step. These two foams work in concert with every stride—the white foam absorbs shock, while the yellow gives just enough bounce that you don’t feel stuck when your foot lands. That firmer foam is key because there’s no plate inside the shoe, as Brooks wanted runners to experience the full feel of foam. “We’ve been having two conversations on foams over the past five years. It’s sort of been like speed foam or cushion foam, because there’s super speed shoes, and then there’s the super cushioned training shoes. Even we talked about them as different foams,” says Caprara. “And what we realized was, that when we started getting to a certain point, you need both. You need some characteristics of your speed foam, and you need some characteristics of your cushion foam.” This exact balance, of softness without sucking away your energy, was the art of building this shoe. Its marginal energy return is about improving sensation rather than speed. The Glycerin Max becomes a truly lovely shoe to run in because it’s so sympathetic to the aches and pains of aging joints, and Caprara has told me for the better part of a year that the prototypes have already become his go-to running shoe. Liberating the foot But you can’t study what’s quickly approaching a decade of maximal shoe designs, and not wonder if we started to reach the mechanical limits of this technology. Are we reaching that point where we won’t see more significant gains in speed or comfort without shifting a paradigm? Caprara calls this phenomenon “the asymptote of maximalism,” and he agrees, based upon materials alone, there’s not much more performance that can be extracted from the tall stack of foam approach. “We’ve gotten to a place where the mechanical component of the shoe has become 95% of the experience,” Caprara says. “And whenever we go to those extremes—away from where the body is driving shoe, [because] now we’re in this mode of the shoe driving the body—we’ve got to liberate the foot again.” And so the future Brooks is building toward now is one that marries the best benefits of a thick foam stack with the more flexible and free footfalls you get with a less rigid shoe. “It’s going to be light,